Activated carbon from admixture of coking coal and inorganic potassium salts

ABSTRACT

Coking coal is admixed with a small but critical amount of inorganic potassium salt, followed by subjecting the mixture to a carbonization to produce a coke which is convertible to activated carbon showing a strong absorption capacity in gas phase.

United States Patent Nishino et a1.

ACTIVATED CARBON FROM ADMIXTURE OF COKING COAL AND INORGANIC POTASSIUMSALTS Inventors: I-Iiroshi Nishino, Nishinomiya;

I-Iakaru Kubo, Takatsuki; Hirohiko Ichlkawa, Kyoto, all of Japan TakedaChemical Industries, Ltd., i-Iigashi-ku, Osaka, Japan Filed: Mar. 9,1971 Appl. No.2 122,548

Related US. Application Data Continuation-impart of Ser. No. 37,441, May15, 1970, abandoned, which is a continuation of Ser. No. 663,220, Aug.25, 1967, abandoned.

Assignee:

U.S.Cl ..2s2/447,252/425,252/445 Int. Cl. C011) 31/08, C01b 31/12, B01j11/06 Field of Search 252/447, 445, 425, 252/421, 422

References Cited UNITED STATES PATENTS l/1970 Fujiwara et al. 252/425FOREIGN PATENTS OR APPLICATIONS 129,083 10/1932 Netherlands..... 252/421291,043 3/1929 Great Britain... 252/422 500,981 6/1930 Germany 252/421506,522 9/1930 Germany 252/425 588,811 6/1947 Great Britain 252/425Primary Examiner-Daniel E. Wyman Assistant Examiner-P. E. KonopkaAttorney -Wenderoth, Lind & Ponack [57] ABSTRACT Coking coal is admixedwith a small but critical amount of inorganic potassium salt, followedby subjecting the mixture to a carbonization to produce a coke which isconvertible to activated carbon showing a strong absorption capacity ingas phase.

6 Claims, No Drawings ACTIVATED CARBON FROM ADMIXTURE OF COKING COAL ANDINORGANIC POTASSIUM SALTS This is a continuation-in-part of Ser. No.37,441, filed May 15, 1970, now abandoned, which is a continuation ofSer. No. 663,220 filed Aug. 25, 1967, now abandoned.

This invention relates to a novel method for the production of coke,and, more particularly, to a method for the production of coke whichcomprises adding inorganic potassium salt to coking coal, i.e.,cokeforming or coking coal, having a grain size of below 660 microns(IL) and subsequently subjecting the mixture to a low temperaturecarbonization.

In hitherto-known methods, the production of activated carbon from coalhas been accompanied with various disadvantages, e.g., weak adsorptioncapacity of activated carbon, requirement of many troublesome processesfor its production, etc. As coal is relatively cheap, the successfulproduction of activated carbon of high quality from coal is adesideratum in many industrial fields.

Activated carbon of high quality can be produced by using the specificcoke obtained by (l) employing coking coal, the grain size of which isbelow 660 p. as the starting material, (2) adding inorganic sodium saltto said coking coal, and (3) subjecting the mixture to a low temperaturecarbonization. Thus-produced activated carbon has a strong adsorptioncapacity in the liquid phase, but is not so strong in adsorptioncapacity in the gas phase. Therefore the said activated carbon cannotadvantageously be applied to technical fields requiring a strongadsorption capacity in the gas phase.

One of the objects of this invention is to provide a method forproducing a specific coke which shows a strong latent adsorptionstructure and can be converted to activated carbon having strongadsorption capacity, especially in the gas phase. This object isrealized by adding 0.8 to 2.5 percent by weight of inorganic potassiumsalt to coking coal having a grain size of below 600 p. and subsequentlysubjecting the mixture to a low temperature carbonization.

Otherwise stated, activated carbon produced according to this inventionby using inorganic potassium salt in place of inorganic sodium salt inthe abovementioned process has much strong adsorption capacity in thegas phase than that produced by using inorganic sodium salt.

Thus the activated carbon derived fromthe present coke canadvantageously be applied to a technical field to which the activatedcarbon derived from the abovementioned prior coke cannot satisfactorilybe applied.

In the method of this invention, the grain size of the coking coal isone of the most important factors in the realization of the object ofthis invention. The fact is clarified by the following test:

Test

To the respective coking coal shown in the following Table I, there isadded 3 percent by weight of potassium carbonate. The mixture issubjected to carbonization at 600 C for 4 to 5 hours. Thus-obtained cokeis activated by the conventional means for the production of activatedcarbon (steam activation at about 800 to 1,000 C), whereby activatedcarbon is produced. The adsorption capacity of thus-produced activatedcarbon is examined by the following method:

a. Test of adsorption capacity by employing acetone Dry air whichcontains 37.5 grams of acetone per cubic meter is passed throughactivated carbon at a thermostat-controlled temperature of 25 C. Theinflow is continued until the equilibrium state is attained. Theadsorption capacity of the activated carbon is expressed by the weightpercent of acetone adsorbed.

b. Test of adsorption capacity by employing benzene The same procedureas in-Test (a) is carried out using 33.6 grams of benzene per cubicmeter in place From the foregoing results, it is clear that coal ofgrain size smaller than 600 p. can give activated carbon having muchhigher adsorption capacity in comparison with coal of average grain sizelarger than about 600 a. The lower limit of grain size in coal is about10 p. since coal of grain size smaller than 10 u is not practically usedindustrially.

When inorganic potassium salt is not added to the coking coal, theadsorption capacity of the activated carbon does not vary with thedifference of the grain size of the coking coal, but is kept constant(acetoneadsorption capacity 10 percent; benzene-adsorption capacity 11.2percent.

In the present invention, coking coal is used, but upon necessity, thecoking coal may be employed in admixture with non-coking coal or pitch.

In the method of this invention, inorganic potassium salt is added tothe coking coal and intimately admixed therewith. As the inorganicpotassium salt, there is em ployed, for example, potassium hydroxide,potassium carbonate, potassium bicarbonate, potassium sulfate, potassiumnitrate, potassium chloride, potassium bromide, potassium iodide,potassium permanganate, potassium cyanide, potassium bichromate and thelike. A single one or an admixture of two or more of these potassiumsalts is used. The amount of inorganic potassium salt to be added mustbe within the range of from about 0.8 to about 2.5 percent by weight, interms of potassium atom relative to the coking coal. The inorganicpotassium salt is employed in the form of an aqueous solution or in theform of solid.

The following results show the adsorption capacity when the amount ofpotassium atom is altered in various ways:

Test Method To coking coal, the grain size of which is .below 600 ,u.,there is added potassium carbonate in the amount shown in Table 2respectively. Then the mixture is subjected to carbonization at 600 Cfor 4 to 5 hours. Thus-obtained coke is activated by conventional steamactivation. The adsorption capacity of thus-obtained activated carbon isexamined in the same way as set forth above.

The superiority of potassium to sodium salts within the critical rangeis apparent from the following table:

(*1 When sodium carbonate is employed in an amount more than 3.2 percentby weight, the coke produced is not in massive (lump) form but inpowdery form.)

(2 The same procedure as in the Test Method is carried out using sodiumcarbonate in place of potassium carbonate.)

The mixture of the said coking coal and inorganic potassium salt is thensubjected to low temperature carbonization. In the method of thisinvention, elevation of the temperature of the carbonization ispreferably effected gradually. Advantageously the highest temperature ofthe carbonization is at about 900 C, and optimally at about 450-700 C.Time required for the carbonization is generally from about 4 to about20 hours.

Activation of the coke of this invention can also be carried out byconventional so-called steam activation at about 800-l ,000 C. The steamactivation can be carried out by the use of steam only, a mixture ofsteam with air, or a mixture of steam and carbon dioxide, duel gas orthe like.

Activated carbon produced from thus-obtained coke of this inventionshows a strong adsorption capacity, especially adsorption capacity ingas phase, which is of the same magnitude as or even superior to that ofactivated carbon produced from charcoal. Further, the density of theactivated carbon produced from the coke of this invention is about 1.2to 1.5 times as high as that of activated carbon produced from charcoal.Further, the loss of raw material to be purified by the adsorptionprocess using the activated carbon in this invention is small;adsorption equipment is small and the waste content of the activatedcarbon is small. Moreover, the reaction velocity at the production ofactivated carbon from the coal of this invention is about 1.5 to 2.0times as high as that from charcoal.

The following examples are only illustrative and are not meant torestrict the scope of this invention. Throughout the specification, theabbreviations kg, g", ml," cm, m and ,1. represent kilogram(s), gram(s),milliliter(s), centimeter(s), meter(s) and micron(s), respectively.

EXAMPLE 1 A box made from iron (0.1 m X 0.3 m X 0.4 m) is packed with amixture of 5.82 kg of powdery coking coal having a grain size of below600 p. and of 0.18 kg of powdery potassium carbonate, and is heated bymeans of fuel gas until the outer temperature becomes 600 C. Then thebox is subjected to carbonization until the inner temperature of the boxbecomes 550 C, for about 4 hours, whereby 4.3 kg of massive coke isobtained.

EXAMPLE 2 To 5.80 kg of coking coal having a grain size below 600 u,there is added 0.20 kg of powdery potassium nitrate. The mixture istreated in thesame way as in Example 1, whereby 4.2 kg of massive cokeis produced. Thus-produced coke is subjected to steam activation at900-l000 C whereby activated carbon showing acetone-adsorption capacityand benzene-adsorption capacity at 32.0 and 40.0 percent, respectively,is obtained.

EXAMPLE 3 To 3.88 kg of a mixture of coking coal having a grain sizebelow 600 p. and non-coking coal in the ratio of :25, there is added anaqueous solution of 0.12 kg of potassium carbonate, followed by mixingthoroughly. Thus-obtained powder is put into a rotary furnace (0.3 m indiameter; 0.5 m in length) which is heated to 600 C. Carbonization iscontinued until the inner temperature becomes 550 C, for about 4 ours,whereby 2.81 kg of massive coke is obtained.

EXAMPLE 4 To 5.84 kg of coking coal having a grain size below 600 u,there is added 0.16 kg of powdery potassium sulfate anhydride. Themixture is treated in the same way as in Example 1, whereby 4.25 kg ofmassive coke is produced. Activated carbon produced from the said cokeby a similar manner to that of Example 2 shows acetone-adsorptioncapacity and benzene-adsorption capacity at 24 and 28 percent,respectively.

EXAMPLE 5 To 5.86 kg of coking coal having a grain size below 600 u,there is added 0.14 kg of powdery potassium chloride. The mixture. istreated in the same way as in Example 1, whereby 4.20 kg of massive cokeis produced. Activated carbon produced from the said coke showsacetone-adsorption capacity and benzeneadsorption capacity at 26 and31.5 percent, respectively.

EXAMPLE 6 To 5.80 kg of the coking coal having a grain size below 6001.1., there is added 0.20 kg of powdery potassium permanganate. Themixture is heated not higher than C and then treated in the same way asin Example 1, whereby 4.10 kg of massive coke is obtained. Activatedcarbon produced from the said coke shows acetone-adsorption capacity andbenzene-adsorption capacity at 29 and 35.5 percent, respectively.

Activated carbon obtained from the present cokecan be used forrecovering acetone from acetonecontaining air which is generated from,e.g., spinning machines for spinning cellulose acetate fiber by thedry-spinning method employing acetone as solvent. For example, aircontaining acetone (37.5 grams per cubic meter) which is generated froman apparatus (10 tons per day scale) for producing cellulose-acetatefibers by the dry spinning method is passed through a series of threecolumns (each column measuring 7 meters in outside diameter and beingpacked with 7.06 tons of the present activated carbon) at a speed(linear velocity) of 9.275 meters per second, whereby 98 percent of theacetone is recovered.

What is claimed is:

1. Activated carbon produced by steam-activation at about 800 to 1000C.of a carbonized admixture of coking coal having a grain size betweenabout 10 p. to about 600 p. and an inorganic potassium salt, which ad-3. The activated carbon of claim 1, wherein the inorganic potassium saltis potassium carbonate.

4. The activated carbon of claim 1, wherein the inorganic potassium saltis potassium sulfate.

5. The activated carbon of claim 1, wherein the inorganic potassium saltis potassium hydroxide.

6. The activated carbon of claim 1 wherein said admixture of coking coaland inorganic potassium salt is carbonized at 450 to 700C.

2. The activated carbon of claim 1, wherein the inorganic potassium saltis a member selected from the class consisting of potassium hydroxide,potassium carbonate, potassium bicarbonate, potassium sulfate, potassiumnitrate, potassium chloride, potassium bromide, potassium iodide,potassium permanganate, potassium cyanide and potassium bichromate. 3.The activated carbon of claim 1, wherein the inorganic potasSium salt ispotassium carbonate.
 4. The activated carbon of claim 1, wherein theinorganic potassium salt is potassium sulfate.
 5. The activated carbonof claim 1, wherein the inorganic potassium salt is potassium hydroxide.6. The activated carbon of claim 1 wherein said admixture of coking coaland inorganic potassium salt is carbonized at 450* to 700*C.